Clark County, Nevada

Clark County is the southernmost and most populous county in the U.S. state of Nevada, with 2,265,461 residents as of the 2020 census. The county is the location of the state's three largest cities, Las Vegas (the county seat), Henderson, and North Las Vegas, as well as the Las Vegas Strip, Nellis Air Force Base, and Hoover Dam. Clark County has 8,061 square miles (20,880 km²) of land area, roughly the size of New Jersey.

Although the county has 70% of Nevada's population making it the 11th-most populous county in the United States, Clark County covers only 7% of Nevada's land mass. Despite having the name Las Vegas as part of their address, over 1 million residents live in unincorporated Clark County, with municipal services provided by the county. The county plays a role much larger than is typical in the US as it has direct jurisdiction over the Las Vegas Strip and such a large population.

Clark County is governed by the Clark County Commission as its partisan, seven member elected body which enacts ordinances and appoints the county manager to administer the ordinances and daily operations of the county. The Las Vegas Metropolitan Police Department (LVMPD) is a city-county law enforcement agency with jurisdiction over all Clark County, resulting from the merger between the city of Las Vegas’ police department and the county sheriff's office.

Originally occupied by the Southern Paiute people and others, the area became part of the Mexican territory of Alta California—then after the Mexican-American War part of the United States—first as part of the New Mexico Territory, and later the Arizona Territory, before becoming part of Nevada as Lincoln County. Clark County was formed from the southern portion of Lincoln on July 1, 1909.

Las Vegas, the state's most populous city, has been the county seat since its establishment. The county was formed by the Nevada Legislature by splitting off a portion of Lincoln County on February 5, 1909, and was organized on July 1, 1909. The Las Vegas Valley, a 600 sq mi (1,600 km²) basin, includes Las Vegas and other major cities and communities such as North Las Vegas, Henderson, and the unincorporated community of Paradise.

Native Americans lived in the Las Vegas Valley beginning over 10,000 years ago. Paiutes moved into the area as early as AD 700. Previously part of the Mexican Territory of Alta California, the Clark County lands were subsequently traversed by American beaver trappers. Word of their journeys inspired the New Mexican merchant Antonio Armijo in 1829 to establish the first route for mule trains and herds of livestock from Nuevo Mexico to Alta California through the area, along the Virgin and Colorado Rivers. Called the Armijo Route of the Old Spanish Trail, the route was later modified into the Main Route by the passing merchants, trappers, drovers, Ute raiders and settlers over the years by moving to a more direct route. In Clark County it was northward away from the Colorado to a series of creeks, waterholes and springs like those at Las Vegas, to which John C. Frémont added Frémont's Cutoff on his return from California to Utah in 1844.

What is now Clark County was acquired by the United States during the Mexican–American War, becoming part of the northwestern corner of New Mexico Territory. In 1847, Jefferson Hunt and other Mormon Battalion members returning to Salt Lake City from Los Angeles pioneered a wagon route through the County that became the Mormon Road. In 1849, this road became known as the "Southern Route", the winter route of the California Trail from Salt Lake City to Los Angeles during the California Gold Rush. By the mid-1850s, the route now known as the Salt Lake Road in California, and the California Road in Utah Territory, was a wagon trade route between the two. In the mid-1850s, Mormons established a Mormon Fort at Las Vegas. In the 1860s, Mormon colonies were established along the Virgin and Muddy Rivers.

All of the county was part of Mohave County, Arizona Territory, when that Territory was formed in 1863, before Nevada became a state. In 1865, it became part of Pah-Ute County, Arizona Territory. The part of Pah-Ute County north and west of the Colorado River was assigned to the new State of Nevada in 1866; however, Arizona territory fought the division until 1871. Pah-Ute County became part of Lincoln County and the westernmost part became the southernmost part of Nye County.